The field of this invention relates to the recovery of cesium from cesium-bearing minerals such as pollucite. More specifically, this invention relates to an improvement in such recovery processes wherein the cesium ore is roasted with an alkaline flux and then leached with water to extract solubilized cesium.
Liberation of cesium from pollucite or other cesiumcontaining minerals has involved extraction with a strong acid, such as hydrochloric or sulfuric acids, or the roasting of the ore with an alkaline flux to convert the cesium to a watersoluble form, such as cesium chloride or cesium carbonate, followed by a water extraction to solubilize cesium. Processes for the recovery of cesium from pollucite and other cesium-containing minerals were reviewed by J. J. Kennedy in Chemical Reviews, Vol. 23 (1938), Pages 157-163. More recent technical developments were summarized by R. A. Heindl, Bureau of Mines Bulletin 650, "Mineral Facts and Problems" (1970 ed.), pages 527-534.
Alkaline flux roasting processes are described in Dean et al., "Dissolution and Roasting Techniques for Extracting Cesium from Pollucite Ores" (1964), U.S. Dept. of Interior, Bureau of Mines, Report 6387; Arnold, et al., I&EC Process Design and Development (1965) 4:249-254; and Davis and Jones, Bureau of Metals, November, 1966, pages 1203-1206. Useable alkaline fluxes may include CaO/CaCl.sub.2 ; CaCO.sub.3 /CaCl.sub.2 ; NaCl/Na.sub.2 CO.sub.3 ; NaOH/Na.sub.2 CO.sub.3 ; NaOH/NaCl; K.sub.2 CO.sub.3 ; and Na.sub.2 CO.sub.3 with a NaHCO.sub.3 leach. While all of these alkaline fluxes are effective for liberation of the cesium as a soluble chloride, carbonate, or bicarbonate salt, better recoveries appear to be obtained with CaO/CaCl.sub.2 or NaCl/Na.sub.2 CO.sub.3 fluxes, which convert the cesium to a CsCl. Extraction with water under alkaline conditions liberates most of the cesium in solubilized form.
Since pollucite ore contains substantial amounts of other alkali metals besides cesium, such as rubidium, and potassium or sodium, as well as substantial amounts of polyvalent metals, primarily aluminum but also iron, acid leaching results in an extract containing the soluble cesium salt in admixture with other alkali metal and polyvalent metal salts. The efficient recovery of the cesium values from such extracts has therefore presented the art with a difficult problem, since it is desired to obtain the recovered cesium compound in as pure a form as possible for further processing to commercial cesium products, such as cesium chloride, cesium iodide, cesium carbonate, cesium sulfate, and also metallic cesium.
Roasting of pollucite with an alkaline flux followed by extraction under alkaline conditions, as described above, has the advantage that the aluminum and iron remains insolubilized as hydroxides. However, alkaline metals in addition to cesium are solubilized, viz. rubidium, potassium, and sodium. The leaching solution will also contain the calcium, sodium, or potassium salts or hydroxides present in or formed by the roasting fluxes. Therefore, a problem of separating the cesium from other soluble metal salts and hydroxides is also encountered in this recovery process. The solubilized cesium may be precipitated as cesium alum, or it may be extracted with an alkyl phenol. However, these processes have proven to be difficult and expensive for commercial application. There has been a recognized need for an improved process for recovering cesium from pollucite in a highly purified form. The need for such a process improvement has been emphasized in recent years by the increasing uses of cesium and cesium compounds, and by the projected expansion of these uses.